Bug 1368208 - Don't flush layout to determine whether scrollbox scroll buttons should be enabled/disabled. r=mconley
☠☠ backed out by 2d19d1d3f8aa ☠ ☠
authorDão Gottwald <dao@mozilla.com>
Mon, 29 May 2017 20:50:23 +0200
changeset 361123 c0c635e938fa8e84cedec58bfe7b1543a67a7d8e
parent 361122 d594a107a7ad24657a31ed0ccf66498136c17db0
child 361124 84a99d06f8db2902ff4c6b41d9fd2c9f71a4d09d
push id31917
push usercbook@mozilla.com
push dateTue, 30 May 2017 09:14:52 +0000
treeherdermozilla-central@0c712d76d598 [default view] [failures only]
perfherder[talos] [build metrics] [platform microbench] (compared to previous push)
reviewersmconley
bugs1368208
milestone55.0a1
first release with
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nightly mac
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nightly win64
Bug 1368208 - Don't flush layout to determine whether scrollbox scroll buttons should be enabled/disabled. r=mconley MozReview-Commit-ID: GfvqsJbNCCU
toolkit/content/widgets/scrollbox.xml
--- a/toolkit/content/widgets/scrollbox.xml
+++ b/toolkit/content/widgets/scrollbox.xml
@@ -180,57 +180,68 @@
           var innerRect = {};
           innerRect.left = outerRect.left - this._scrollbox.scrollLeft;
           innerRect.top = outerRect.top - this._scrollbox.scrollTop;
           innerRect.right = innerRect.left + this._scrollbox.scrollWidth;
           innerRect.bottom = innerRect.top + this._scrollbox.scrollHeight;
           return innerRect;
         ]]></getter>
       </property>
-      <property name="scrollboxPaddingStart" readonly="true">
-        <getter><![CDATA[
-          var ltr = (window.getComputedStyle(this).direction == "ltr");
-          var paddingStartName = ltr ? "padding-left" : "padding-right";
-          var scrollboxStyle = window.getComputedStyle(this._scrollbox);
-          return parseFloat(scrollboxStyle.getPropertyValue(paddingStartName));
-        ]]></getter>
-      </property>
+      <field name="scrollboxPaddingStart"><![CDATA[
+        let paddingStart = this.orient == "vertical" ? "paddingTop" :
+              (this._isRTLScrollbox ? "paddingRight" : "paddingLeft");
+        parseFloat(window.getComputedStyle(this._scrollbox)[paddingStart]);
+      ]]></field>
+      <field name="scrollboxPaddingEnd"><![CDATA[{
+        let paddingEnd = this.orient == "vertical" ? "paddingBottom" :
+              (this._isRTLScrollbox ? "paddingLeft" : "paddingRight");
+        parseFloat(window.getComputedStyle(this._scrollbox)[paddingEnd]);
+      }]]></field>
       <property name="scrollPosition">
         <getter><![CDATA[
           return this.orient == "vertical" ?
                  this._scrollbox.scrollTop :
                  this._scrollbox.scrollLeft;
         ]]></getter>
         <setter><![CDATA[
           if (this.orient == "vertical")
             this._scrollbox.scrollTop = val;
           else
             this._scrollbox.scrollLeft = val;
           return val;
         ]]></setter>
       </property>
 
-      <property name="_startEndProps" readonly="true">
-        <getter><![CDATA[
-          return this.orient == "vertical" ?
-                 ["top", "bottom"] : ["left", "right"];
-        ]]></getter>
-      </property>
+      <field name="_startEndProps"><![CDATA[
+        this.orient == "vertical" ?
+          ["top", "bottom"] : ["left", "right"];
+      ]]></field>
 
       <field name="_isRTLScrollbox"><![CDATA[
         this.orient != "vertical" &&
         document.defaultView.getComputedStyle(this._scrollbox).direction == "rtl";
       ]]></field>
 
       <field name="_scrollTarget">null</field>
 
       <method name="_canScrollToElement">
         <parameter name="element"/>
         <body><![CDATA[
-          return window.getComputedStyle(element).display != "none";
+          if (element.hidden) {
+            return false;
+          }
+
+          // See if the element is hidden via CSS without the hidden attribute.
+          // If we get only zeros for the client rect, this means the element
+          // is hidden. As a performance optimization, we don't flush layout
+          // here which means that on the fly changes aren't fully supported.
+          let rect = window.QueryInterface(Components.interfaces.nsIInterfaceRequestor)
+                           .getInterface(Components.interfaces.nsIDOMWindowUtils)
+                           .getBoundsWithoutFlushing(element);
+          return !!(rect.top || rect.left || rect.width || rect.height);
         ]]></body>
       </method>
 
       <method name="ensureElementIsVisible">
         <parameter name="element"/>
         <parameter name="aSmoothScroll"/>
         <body><![CDATA[
           if (!this._canScrollToElement(element))
@@ -606,50 +617,86 @@
           if (this._isScrolling) {
             this._scrollAnim.stop();
             this._isScrolling = 0;
             this._scrollTarget = null;
           }
         ]]></body>
       </method>
 
+      <field name="_scrollButtonUpdatePending">false</field>
       <method name="_updateScrollButtonsDisabledState">
-        <parameter name="aScrolling"/>
         <body><![CDATA[
-          let scrolledToStart;
-          let scrolledToEnd;
+          if (this._scrollButtonUpdatePending) {
+            return;
+          }
+          this._scrollButtonUpdatePending = true;
 
-          // Avoid flushing layout when not overflowing or when scrolling.
           if (this.hasAttribute("notoverflowing")) {
-            scrolledToStart = true;
-            scrolledToEnd = true;
-          } else if (aScrolling) {
-            scrolledToStart = false;
-            scrolledToEnd = false;
-          } else if (this.scrollPosition == 0) {
-            // In the RTL case, this means the _last_ element in the
-            // scrollbox is visible
-            scrolledToEnd = this._isRTLScrollbox;
-            scrolledToStart = !this._isRTLScrollbox;
-          } else if (this.scrollClientSize + this.scrollPosition == this.scrollSize) {
-            // In the RTL case, this means the _first_ element in the
-            // scrollbox is visible
-            scrolledToStart = this._isRTLScrollbox;
-            scrolledToEnd = !this._isRTLScrollbox;
+            // Invalidate layout lazily before painting the next frame.
+            window.requestAnimationFrame(() => {
+              this._scrollButtonUpdatePending = false;
+
+              this.setAttribute("scrolledtoend", "true");
+              this.setAttribute("scrolledtostart", "true");
+            });
+            return;
           }
 
-          if (scrolledToEnd)
-            this.setAttribute("scrolledtoend", "true");
-          else
-            this.removeAttribute("scrolledtoend");
+          // Wait until after the next paint to get current layout data from
+          // getBoundsWithoutFlushing.
+          window.requestAnimationFrame(() => {
+            window.requestAnimationFrame(() => {
+              this._scrollButtonUpdatePending = false;
+
+              let scrolledToStart = false;
+              let scrolledToEnd = false;
+
+              if (this.hasAttribute("notoverflowing")) {
+                scrolledToStart = true;
+                scrolledToEnd = true;
+              } else {
+                let scrollboxPaddingStart = Math.round(this.scrollboxPaddingStart);
+                let scrollboxPaddingEnd = Math.round(this.scrollboxPaddingEnd);
+                let [start, end] = this._startEndProps;
+                if (this._isRTLScrollbox) {
+                  [start, end] = [end, start];
+                  scrollboxPaddingStart = -scrollboxPaddingStart;
+                  scrollboxPaddingEnd = -scrollboxPaddingEnd;
+                }
 
-          if (scrolledToStart)
-            this.setAttribute("scrolledtostart", "true");
-          else
-            this.removeAttribute("scrolledtostart");
+                let windowUtils = window.QueryInterface(Components.interfaces.nsIInterfaceRequestor)
+                                        .getInterface(Components.interfaces.nsIDOMWindowUtils);
+                let rect = ele => windowUtils.getBoundsWithoutFlushing(ele);
+                let scrollboxRect = rect(this._scrollbox);
+                let elements = this._getScrollableElements();
+                let [firstElement, lastElement] = [elements[0], elements[elements.length - 1]];
+
+                if (firstElement &&
+                    rect(firstElement)[start] - scrollboxPaddingStart == scrollboxRect[start]) {
+                  scrolledToStart = true;
+                } else if (lastElement &&
+                           rect(lastElement)[end] + scrollboxPaddingEnd == scrollboxRect[end]) {
+                  scrolledToEnd = true;
+                }
+              }
+
+              if (scrolledToEnd) {
+                this.setAttribute("scrolledtoend", "true");
+              } else {
+                this.removeAttribute("scrolledtoend");
+              }
+
+              if (scrolledToStart) {
+                this.setAttribute("scrolledtostart", "true");
+              } else {
+                this.removeAttribute("scrolledtostart");
+              }
+            });
+          });
         ]]></body>
       </method>
     </implementation>
 
     <handlers>
       <handler event="wheel"><![CDATA[
         let doScroll = false;
         let useSmoothScroll = event.deltaMode != event.DOM_DELTA_PIXEL && this.smoothScroll;
@@ -792,37 +839,17 @@
           // as the whole overflow event should not be happening in that case.
           this._updateScrollButtonsDisabledState();
         } catch (e) {
           this.setAttribute("notoverflowing", "true");
         }
       ]]></handler>
 
       <handler event="scroll"><![CDATA[
-        if (!this._delayedUpdateScrollButtonsTimer) {
-          // This is the beginning of a scrolling animation. We need to update
-          // scroll buttons now in case we were scrolled to the start or to the
-          // end before we started scrolling.
-          this._updateScrollButtonsDisabledState(true);
-        } else {
-          // We're in the middle of the scrolling animation. We'll restart the
-          // delayed update request so that we only update the scroll buttons
-          // a second time once we're done scrolling.
-          window.clearTimeout(this._delayedUpdateScrollButtonsTimer);
-        }
-
-        // Try to detect the end of the scrolling animation to update the
-        // scroll buttons again. To avoid false positives, this timeout needs
-        // to be big enough to account for intermediate frames that don't move
-        // the scroll position in case we're scrolling slowly.
-        this._delayedUpdateScrollButtonsTimer = setTimeout(() => {
-          // Scrolling animation has finished.
-          this._delayedUpdateScrollButtonsTimer = 0;
-          this._updateScrollButtonsDisabledState();
-        }, 200);
+        this._updateScrollButtonsDisabledState();
       ]]></handler>
     </handlers>
   </binding>
 
   <binding id="autorepeatbutton" extends="chrome://global/content/bindings/scrollbox.xml#scrollbox-base">
     <content repeat="hover">
       <xul:image class="autorepeatbutton-icon"/>
     </content>